Patent GB-1418519-A (GB)
Title: Pressure sensitive semiconductor device and method of manufacture  thereof
IPC: H01L29/267
Filed: 1973-03-21
Abstract: 1418519 Semiconductor electromechanical transducers OMRON TATEISI ELECTRONICS CO 21 March 1973 [21 March 1972] 13590/73 Heading H1K An electromechanical transducer (Fig. 1) comprises a N-type Si monocrystal substrate 1 with a layer 2 of SiO 2  thereon overlain with a layer 3 of SnO 2  constituting an N-type semiconductor. A metal electrode 5 underlies the substrate and an electrode 4 overlies part of layer 3 with an ammeter and reverse bias voltage in series across the electrodes. Mechanical pressure is applied over a glass or metal rod with a spherical tip bearing on layer 3, to vary reverse current. The composite has a rectifying characteristic and exhibits photoelectric properties to radiation applied to the hetero junction within the composite. . In fabrication (Fig. 2) a quartz tube 21 encircled by an electric heater 22 has tube 11 supplying oxygen or air controlled by valves 13, 29 and flow meter 12, a tube 18 supplying water vapour from evaporator 17, and tube 15 supplying a gaseous mixture of (CH 3 ) 2 SnCl 2  and inert gas through evaporator 14 and valve 16 under control of valves 29<SP>1</SP>, 13<SP>1</SP> and flow meter 12<SP>1</SP>. Exhaust gas emerges from exit 27 at a controlled rate, and in the tube 21 a quartz support carries Si wafer 1. The wafer is initially polished or rough finished, washed in HF, and inserted in the reaction zone, heated to working temperature, and the oxident and the water vapur are fed in. An SiO 2  film forms on the surface and its thickness is controlled by varying temperature and/or exposure time. Thereafter preheated inert gas and organic tin vapour are admixed and admitted at reduced pressure due to vacuum exhaustion of outlet 27. Prolysis and oxidation of the admixed gas deposits a transparent conductive SnO 2  film on the SiO 2  film, and conductivity is improved by addition of SbCl 3  into the gas mixture. Substrate may be P-type Si, Ge, or GeAs and SiO 2  is replaceable by Si 3 N 4  or GeO 2  as insulant. An alternative device (Fig. 3) comprises annular SiO 2  layer 2<SP>1</SP>, a further film 2 thereof deposited in the aperture thereof, and SiO 2  film 3 depositied on films 2, 2<SP>1</SP> with an electrode 4 thereupon.  Rectifying, statistical breakdown distribution with reverse voltage, reverse leakage current and reverse breakdown voltage related to film thickness are discussed and compared with similar characteristics of prior art devices with SnO 2  directly overlying Si without illumination or application of mechanical force (Figs. 4 to 7, not shown). The reverse current is shown to be linearly related to the mechanical force applied for constant energization voltage with sensitivity critically dependent on SiO 2  film thickness (Figs. 8, 9, 10, not shown). A modified transducer (Fig. 11, not shown) may be pressurized by a spherical member and (Fig. 12, not shown) by using a substrate with an uneven surface produced, e.g. by etching on the SiO 2  and SnO 2  layers are applied. Greater sensivitivity of response of reverse current to applied pressure is obtained due to shear deformation (Fig. 13, not shown). A theoretical explanation is given. A further modification (Fig. 14) comprise a substrate 51 presenting mesas divided by a lattice of etched grooves 50 with insulant film 52 of, e.g. Si 3 N 4  deposited on the peaks (which may be used to mask the groove etching). A SiO 2  film 54 and SnO 2  film 53 are deposited on the surface including the grooves. In further modifications the device of Fig. 1 may be exposed to light applied through the SnO 2  film to give photoelectric response, and (Fig. 15, not shown) an obturating layer, e.g. of N may overly the SnO 2  layer 3 (Fig. 3) to exclude light and also serve as an electrode. The obturant layer may alternatively be of Mo, Wo, Pt, Cr or of Al 2 O 3 . Where the substrate is uneven its crystallographic plane is unimportant, but where it is polished, senstitivity and stability are improved using a (100) plane instead of a (111) plane. Pressure resistivity diminishes and stability of reverse current is improved with increasing specific resistivity of substrate. Reference has been directed by the Comptroller to Specification 1,328,707.